1. Technical Field
The present disclosure generally relates to image forming apparatuses, and more specifically an image forming apparatus including a head part having a jet opening configured to jet ink, a moisture retention cap configured to maintain moisture by closing the jet opening part, and a suction part configured to suction ink situated at the jet opening part.
2. Description of the Related Art
An inkjet printer as an image forming apparatus which jets an ink drop from a jet opening part of a head part so as to form an image on a recording medium is well known. A water type ink composed of a pigment and a solvent wherein a wetting agent (humectant) and penetrating agent are included in water, is used as ink liquid for such an inkjet printer. In an inkjet printer using the ink liquid, ink viscosity is increased due to evaporation of the ink solvent at a head jet opening so that the jet opening is clogged up or closed due to the adhesion of dust and thereby an image is degraded. In order to solve such a problem, Japan Laid-Open Patent Application Publications No. 2002-361905, No. 2003-1839, and No. 2003-1832 suggest a structure where a cap member for capping a head at the time of non-image forming so that moisture of a head jet opening is maintained and a suction mechanism such as a suction pump, provided at the cap member, for suctioning dust adhered to the jet opening together with the ink are provided. Thus, it is possible to prevent the increase of ink velocity.
By capping the head jet opening, ink viscosity is prevented from being increased due to the evaporation of the ink solvent at the head jet opening so that the jet opening is prevented from being clogged up. In addition, the dust adhered to the jet opening is suctioned together with the ink by the suction pump, so that the jet opening is prevented from being closed.
However, in the above-mentioned related arts disclosures, the ink suctioned by the suction pump is adhered to an internal wall surface of the cap member. Thus, if the head is capped in a state where the ink is adhered to the internal wall surface, the viscosity at the head jet opening is increased while the head jet opening is capped by the cap member. This causes an evaporation component such as water of the ink drop adhered to the internal wall surface of the cap member to evaporate when the cap member is opened, so that the ink drop, wherein the evaporation component adhered to the internal wall surface of the cap member evaporates, absorbs the evaporation component situated at the ink jet opening. As a result of this, the viscosity at the head jet opening is increased. Particularly, in a case where the ink liquid has a high viscosity, the image is influenced even if the viscosity at the head jet opening is slightly increased. Because of this, preliminary jetting is performed in order to adjust the viscosity of the jet opening and ink meniscus before printing starts. However, in order to adjust the viscosity of the jet opening, it is necessary to jet a lot of ink drops. Because of this, a lot of, from ten and several to several thousands, ink drops are jetted from a single jet opening for every preliminary jetting prior to start of the printing. This causes an increase in consumption of the ink.
The assignee of the present application suggests a structure where a moisture retention cap for maintaining moisture of the head jet opening and a suction cap for suctioning ink at the head jet opening are provided so that the viscosity of the ink is prevented from being increased at the time of moisture retention at the jet opening.
In a case where the moisture retention cap and the suction cap are separately provided, the suction cap is in a state where the suction cap is opened other than when the suction cap is suctioning the ink situated at the head jet opening. Because of this, a foreign body such as the dust enters into the suction cap and the dust is pulled into the suction tube and thereby it may not be possible to obtain a sufficient suction force due to closure of the flow path. In order to solve such a problem, a structure where a shutter member for covering an opening part of the suction cap at the time of non-operation of the suction means is provided is suggested at Japanese Patent Application No. 2004-184500. However, in the structure where the opening part of the suction cap is merely covered with the shutter member, a foreign body such as dust may enter into the suction cap via a gap between the opening part of the suction cap and the shutter member. Because of this, the dust may be pulled into the suction tube so that the flow path is closed and therefore sufficient suction force may not be obtained.